I do what other U.S. native speakers do. I use a dictionary. Before computers, any educated U.S. speaker would keep a desk dictionary within easy reach. A lot of people still do.
I use a dictionary to check pronunciations probably once a month. I should do it more often.
I sometimes--rarely, but sometimes--make embarrassing mistakes in pronunciation. When I was a grad student, some of my work involved a species of animal whose scientific name is Tripneustes. For years, I thought the name was Tripnuestes and pronounced it "TRIP-new-ESS-tees." During my thesis defense I pronounced it that way, and a professor coughed and said, "I think that is 'try-NOOSE-tees.'" I passed the defense, but ever since then I've been more careful.
Of course, often, I will just guess. After six decades of using English, I am a good guesser, and--what's more important--fairly good a judging _whether it is safe to guess._ For example, if I see that a part of an airplane is an "empennage," without even thinking about it I recognize it as one of those French-derived aviation words and know that "-age" should be "-azh," as in "fuselage" or "garage;" not "-idge" as in "message" or "cribbage," and not like the word "age" as in "stage" or "rampage."
If I were reading, I'd just guess at the pronunciation of "empennage" and go on reading. But if I knew I would need to say it aloud in front of people, I would check a dictionary.
English speakers need dictionaries to check pronunciations. That's just the way it is.